1. Field of the Invention
The present invention relates to a magnetic recording medium including a recording layer formed in a predetermined concavo-convex pattern in which recording elements form convex portions, and a magnetic recording and reproducing apparatus including that magnetic recording medium.
2. Description of the Related Art
Conventionally, in a magnetic recording medium such as a hard disk, various types of development such as miniaturization of magnetic particles forming a recording layer, change of a material for the magnetic particles, and miniaturization of head processing have been made to largely improve areal density of the recording layer. The improvement of the areal density is expected to continue. However, many problems including the limitation of the magnetic head processing, improper recording of information onto a track adjacent to a target track caused by broadening of a magnetic field, crosstalk during reproducing, and the like are made apparent. Thus, the improvement of the areal density by the conventional development approach has reached the limit.
Therefore, a magnetic recording medium such as a discrete track medium and a patterned medium, that includes a recording layer formed in a concavo-convex pattern in which recording elements form convex portions, has been proposed as a candidate of a magnetic recording medium that enables further improvement of the areal density (see Japanese Patent Laid-Open Publication No. Hei 9-97419, for example). As the areal density becomes higher, the magnetic gap between a magnetic head and a magnetic recording medium becomes smaller. Thus, in case of a magnetic recording medium that is expected to have the areal density of 200 Gbpsi or more, such as a discrete track medium or a patterned medium, a guideline is issued that the magnetic gap between the magnetic head and the magnetic recording medium should be set to 15 nm or less.
Moreover, in a magnetic recording medium such as a hard disk, flatness of its surface is important in order to suppress crash of the magnetic recording medium against the magnetic head. The flatness of the surface is more important especially in a discrete track medium or a patterned medium that has high areal density and a small magnetic gap. Thus, it is preferable to fill concave portions between recording elements with a non-magnetic filling element and flatten a top surface of the recording elements and filling elements. Deposition methods such as sputtering, CVD(Chemical Vapor Deposition), and IBD (Ion Beam Deposition) can be used for filling the concave portions with the filling element. Moreover, processing methods such as CMP (Chemical Mechanical Polishing) and dry etching can be used for flattening the top surface of the recording elements and filling elements (see Japanese Patent Laid-Open Publication No. Hei 12-195042 and Japanese National Publication of PCT application No. 14-515647, for example).
However, when the surface of the magnetic recording medium is excessively flat, stiction of the magnetic head onto the surface of the magnetic recording medium can easily occur and therefore crash of the magnetic recording medium against the magnetic head can easily occur. In order to prevent the crash caused by the head stiction, according to the conventional technique, a texture process is performed for a surface of a substrate and a recording layer and other layers are sequentially deposited over that surface, thereby forming a fine concavo-convex pattern on the surface of the magnetic recording medium to follow the texture pattern on the substrate (see U.S. Pat. Nos. 5,499,731, 5,714,207, for example). Moreover, in case of a discrete track medium or a patterned medium, a structure is known in which a step is provided between the top surface of the recording elements and the top surface of the filling elements (see Japanese Patent Laid-Open Publication No. Hei 1-279421, for example). This step provides a texture effect.
However, when the fine concavo-convex pattern is formed on the surface of the magnetic recording medium by performing the texture process for the substrate, distortion like undulation having a period of about 100 nm to about 2 μm occurs on the surface of the magnetic recording medium. It is difficult for the magnetic head to follow and fly above the undulation-like distortion having the above period. Moreover, that distortion directly leads to variation in the size of the magnetic gap. In a magnetic recording medium of an earlier generation for which the magnetic gap of 25 nm or more is ensured, the aforementioned variation in the size of the magnetic gap does not matter practically. However, in a magnetic recording medium having the magnetic gap of 15 nm or less, the aforementioned variation in the size of the magnetic gap has effects that are practically unacceptable.
Moreover, even if the texture process is performed for the surface of the substrate, when spaces between the recording elements are filled with the filling element and the top surface of the recording elements and filling elements is flattened, the fine concavo-convex pattern following the texture pattern on the substrate is removed. Thus, it is difficult to form a fine concavo-convex pattern in a desired manner on the surface of the magnetic recording medium by using the technique of performing the texture process.
Furthermore, in the technique of forming the steps between the top surface of the recording element and the top surface of the filling element, the flying of the magnetic head becomes unstable because the rigidity of an air layer between the magnetic head and the surface of the magnetic recording medium becomes excessively small. Thus, the flying height of the magnetic head can be easily and largely changed by external disturbance and therefore sufficient reliability cannot be achieved.